Recently, bi-tubular or mono-tubular type color television camera tubes have been developed as components for prior multi-tubular type color television camera tubes. An example of these types of television camera tubes is a multicolor optical filter plate which comprises an optically abraded glass disk plate, a filter comprising multicolor stripes containing organic dyes or a cross pattern of striped filter elements formed on the glass disk plate and a glass thin layer having a thickness of about 10 to 30 .mu.m formed thereon. A transparent electrode layer and a photoconductive layer for picking up color signals passing through the filter are provided in a body on the thin glass layer of this multicolor optical filter plate to form a face plate for the color television tube. The multicolor optical filter conventionally used here is one wherein three colors consisting of red, green and blue or cyan, magenta and yellow are regularly arranged. But the color composition thereof is not limited to the above described three colors, and there are those having two colors or four or more colors.
The most conventional process for producing color filter plates for color television camera tubes is described in the following. This process is illustrated with reference to FIG. 1 which shows the structure of the prior multicolor optical filter plate for color television camera tubes. A multicolor optical filter layer 11 is formed on an optically abraded glass disk plate 10 by, for example, the following process. After a thin glass plate 13 is adhered to the layer 11 with an adhesive 12, the thin glass plate 13 is abraded to be even thinner (to a thickness of about 10 to 30 .mu.m or so) to produce a multicolor optical filter plate. On the thin glass plate of the resulting filter plate, a transparent electrode layer and a photoconductive layer are provided by, for example, vacuum evaporation to produce a face plate for the color television camera tube. The reason why the thin glass plate is provided between the multicolor optical filter layer 11 and the transparent electrode layer is as follows. Namely, where the multicolor optical filter layer 11 contains organic dyes, it is necessary to prevent the influence caused by generation of a gas deleterious in taking a picture from the filter layer, when the transparent electrode layer and the photoconductive layer are deposited by vacuum evaporation or the resulting face plate for the color television camera tube is used. Further, the reason why the thickness of the thin glass plate is reduced by abrading is to prevent formation of dim images as far as possible where rays passing through the color filter are focused on the photoconductive layer.
However, inevitably the color filter plate thus obtained becomes naturally expensive because the steps for forming a desired pattern on the color filter layer is very complicated. Namely, known color filters are those using a dichroic film (an interference membrane process) as described in, for example, Japanese Patent Publication No. 8590/65 and Japanese Patent Application (OPI) No. 3440/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") and those prepared by dyeing a high molecular weight material layer with dyes (a dyeing process) as described in, for example, Japanese Patent Application (OPI) Nos. 37237/72, 63739/73 and 66853/73 and Japanese Patent Publication No. 248/78. However, the processes for producing them are very complicated and troublesome, because they require the steps of pattern formation including coating of a photoresist, imagewise exposure with precise arrangement of a mask, development, coloration or bleaching and removal of the resist, etc., for every color, and these steps must be repeatedly carried out many times (generally 3 times or more).
Some of the present inventors have developed various processes for producing color filter patterns in a simple manner using a silver halide emulsion as a material for forming a filter layer. One of these processes is that described in U.S. Pat. No. 4,271,246. This process comprises, as essential steps, carrying out a pattern exposure for the first color of a black-white silver halide emulsion layer in a photographic material comprising a support and at least one black-white silver halide emulsion layer provided on the support, forming a pattern containing a dye of the first color by color development with a developer containing a color coupler, carrying out a pattern exposure for the second color of the unexposed part containing silver halide, forming a pattern containing a dye of the second color by color development with a developer containing a color coupler, and, if necessary, repeating the same steps for forming a pattern containing a dye of third or subsequent colors, to form an image composed of at least two colors, and removing silver after the final color development to produce a multicolor optical filter. Further, if a silver halide emulsion is used as a material for forming the filter layer, it is possible to adopt any process for development which has been used for color photography.
When the silver halide emulsion is used as the material for forming the filter layer, not only can color filters be produced less expensively as compared with the above described prior interference membrane process or dyeing process but also there is the following advantage. Namely, the silver halide emulsion is not formed on a disk plate for the television camera tube but is applied to a thin plate of glass, etc., which is sufficiently larger than the disk plate, and a plurality of color filters is then formed at the same time on a single glass plate by the above described process. The glass plate is then cut to have each individual color filter thereon and is adhered to each glass disk plate. Since a plurality of color filters is formed at the same time on a single glass plate as described above, it becomes possible to obtain a number of color filters at the same time. Further, if a defective filter is produced therein, the filter only needs to be discarded. Accordingly, the cost per filter plate becomes remarkably low in forming the filter on an expensive optically abraded glass disk plate, because the step of reproducing the glass disk plate can be omitted where defective filters are formed.
It has, however, been found that the following disadvantage occurs when the color filter plate is produced by a process which comprises forming a color filter pattern on a silver halide emulsion layer provided on a transparent support of glass, etc., adhering a transparent plate of glass, etc., thereto with an adhesive (after the transparent support has been cut into each filter part where a plurality of patterns is formed on the transparent support such as a thin glass plate, etc., which is sufficiently larger than the glass disk plate), and thereafter reducing the thickness of the transparent plate or the transparent support by abrasion. Namely, in reducing the thickness of the above described transparent plate or the transparent support by abrasion, the abrasion is generally carried out in the presence of water. In such case, water permeates at the edges of the emulsion layer placed between the transparent plate and the transparent support and the binder (generally gelatin) of the emulsion layer swells, by which the edges of the transparent plate or the transparent support are broken due to the force of expansion during abrading when the transparent plate or the transparent support becomes thin as abrasion progresses. Although this damage of the edges of the transparent plate or the transparent support does not directly influence the color filter pattern area, the organic material (gelatin) is exposed at the broken areas and, consequently, difficulty in vacuum sealing occurs, because there is the possibility of generation of noxious gas from the filter layer when the transparent electrode layer and the photoconductive layer are deposited by vacuum evaporation or the resulting face plate for the color television camera tube is used.